Diamond Deposition Research Articles

Direct-drive implosion experiment of diamond capsules fabricated with hot filament chemical vapor deposition technique

Diamond is a promising alternative capsule material for direct-drive inertial confinement fusion. Previous investigations suggest that the stiffness and higher density of diamond can mitigate laser imprinting, which is an initial perturbation on the ablation surface caused by non-uniform laser irradiation. We conduct diamond capsule fabrication using the hot filament chemical vapor deposition (HF-CVD) technique. This technique is the most suitable diamond deposition method in terms of mass production, since the deposition area can be easily extended just by increasing the number of hot filaments. This paper presents the first direct-drive implosion experiment concerning diamond capsules fabricated using the HF-CVD technique. The compression of thin diamond capsules, with an inner capsule diameter of 482 μm and a shell thickness of 1.6 μm, is successfully achieved, and the implosion trajectory of diamond capsules, with the same diameter and thickness, is consistent with 1D radiation hydrodynamic simulation calculations. However, for diamond capsules with an inner diameter of 482 μm and a shell thickness of 2.4 μm, asymmetry of the implosion trajectory and unexpected x-ray emission are observed. This is attributed to the remaining silicon (Si) mold inside the capsule left over from the fabrication process, revealing that the etching method of Si in diamond capsules should be improved.

Radiation and physical parameters of kimberlites and host rocks of the Lomonosov diamond deposit (Russian North-West)

In this paper, experimental studies of rocks were carried out to assess the main radiation and physical factors affecting the formation of the radon field over the kimberlite pipes of the Arkhangelsk diamondiferous province (for example, the Lomonosov diamond deposit). For various types of rocks, the following was studied: porosity, density, radium-226 activity, free radon activity, radon production rate, emanation coefficient. The research results showed that the main factors in the formation of the radon field are porosity and the coefficient of emanation. These parameters directly affect the amount of free radon. In addition, we calculated the radon production by various types of rocks, represented by vent kimberlites, tuffaceous-sedimentary rocks of the crater, enclosing and overlying sediments. Regression analysis showed that the radon production rate in rocks reflects the formation of a radon field under conditions of occurrence of a kimberlite body. The studied radiation and physical parameters showed that the greatest amount of radon in a free state is produced by rocks of the near-pipe space, represented by the enclosing Vendian V2 deposits and characterized by high values of the emanation coefficient, specific activity of radium, the radon production rate, and porosity. At the same time, the formation of free radon in the tube body is limited due to the low values of porosity, emanation coefficient, and the radon production rate.

More on Diamonds and De Beers

The author develops and supplements his previous analysis of a long period of Moscow’s confidential cooperation with South African diamond cartel De Beers, both forced and mutually beneficial, initially in the 1920s, then from late 1950s to early 1990s (Journal of the Institute for African Studies №3(40),2017). According to recently released documents such cooperation also continued between these two periods. It provided Soviet enterprises with imported industrial diamonds for precision instruments and augmented the country’s defense potential during the period of toughest Western Cold war sanctions in 1949–1953, before the discovery and extraction of rich deposits of Yakut diamonds. The article contains some interesting evidence of Russian diaspora involvement in South African industrial development. The author also calls for greater objectivity in historic analysis of the period of South African internal colonialism and anti-apartheid struggle.

Dissociative electron attachment in C2H via electronic resonances

Investigation of microwave-activated CH/H plasma used in chemical vapour deposition of diamond revealed the presence of electronically excited C (B). Using high-level electronic structure methods, we investigate electronic structure of CH and suggest possible routes for the formation of C in the ground (X) and excited (B) states via electronic resonances. To describe electronically metastable states, we employ the equation-of-motion coupled-cluster method augmented by the complex absorbing potential. The resonance wavefunctions are analysed using natural transition orbitals. We identified several resonances in CH, including the state that may lead to C (B).

Diamondiferous kimberlites from recently explored Upper Muna Field (Siberian Craton): petrology, mineralogy and geochemistry insights

Abstract Petrographic, geochemical and mineralogical characteristics of diamond deposits from the Upper Muna field have been investigated. Geochemically, diamondiferous kimberlites from Upper Muna belong to the most widespread Fe–Mg-rich rocks in the Yakutian kimberlite province (average FeO total = 8.4 wt%, MgO = 32.36 wt%, TiO 2 = 1.6 wt%). Striking mineralogical features of Upper Muna kimberlites are: (1) abundance of monticellite and perovskite in the groundmass; (2) rare occurrence of Mg-ilmenite; (3) abundance of phlogopite megacrysts (up to 8 cm across); and (4) coexistence of low-Cr (0.1–4 wt% Cr 2 O 3 , with 0.8–1.2 wt% TiO 2 ) and high-Cr (3–8 wt% Cr 2 O 3 , with 0.1–0.6 wt% TiO 2 ) garnet megacrysts with contrasting rare earth element patterns. The compositional features of groundmass minerals, the relatively low CaO and CO 2 contents in kimberlites and few deuteric alteration in Upper Muna kimberlites suggest high-temperature melt crystallization during pipe emplacement. Based on the compositional data of garnet and Cr-diopside from megacrysts and peridotites, we suggest a poor Cr dunite–harzburgitic and lherzolitic mantle source beneath the Upper Muna field where Cr-diopside crystallized within a wide pressure and temperature range (40–65 kbar and 900–1350°С). The mineral geochemistry, trace element distribution and Sr–Nd isotope variations of Upper Muna kimberlites are typical for group I kimberlites and reflect a deep-seated asthenospheric (convective mantle) source for the kimberlites.

Artisanal mining, mechanization and human (in) security in Sierra Leone

In recent years, as alluvial mineral deposits in many regions of West Africa have become ‘worked out’, new methods of extraction have become increasingly prevalent. In the case of Sierra Leone, traditional artisanal and small-scale mining (ASM) employing rudimentary hand tools has gradually become more mechanized, with the illicit use of heavy machines outpacing the development of laws and policies aimed at regulating them. Drawing on field-based research undertaken in diamondiferous Kono District in Sierra Leone's Eastern Province, this paper explores the political economy underpinning the mechanization of ASM, as well as its implications for human security. Popular discourse has frequently employed technical narratives to explain the drivers of mechanization, including dwindling alluvial diamond deposits, unreliable geological data and the weak law enforcement capacity of regulatory agencies. This paper, however, contends that the mechanization of ASM is also an elite adaptation strategy through which modes of production are effectively controlled. This process is deeply political and divisive, resulting in the (re)production of winners and losers. As inequality between elite actors and dispossessed diggers has deepened, the resulting human security challenges of mechanization are immense—including undervalued and dislocated labor, rapid environmental degradation, and the widespread destruction of livelihoods. A shift in mining policy and law that is likely to address the human security impacts currently unravelling in ASM communities, should be preceded by a grounded, cost-benefit analysis, in order to determine the potential winners and losers, and to inform more sustainable design and implementation.

Ferruginous duricrusts associated with diamond occurrences in the Diamantina Plateau, south Espinhaço Range, Brazil

Macromorphological and micromorphological characterization of the alteration facies associated with geomorphological studies are of great importance for understanding the genesis and evolution of ferruginous duricrusts. The study of the ferruginous duricrusts in the Diamantina Plateau (Southern Espinhaço Range, Minas Gerais), a region known worldwide for hosting important diamond deposits, was based on the characterization of the faciological variations of representative alteration profiles. The morphometric indexes of the area, macromorphological description of the profiles, and sampling for micromorphological and mineralogical analyzes were carried out to assist in the understanding of the landforms. The results show that the ferruginous duricrusts occur preferentially in the plateaus and high slopes, with the Sopa-Brumadinho Formation as substrate. Two types of ferruginous duricrust have been identified. Type 1 is characterized as a platy duricrust developed from a saprolite of hematitic phyllite with a ferruginous banded structure. Type 2 is characterized by a massive duricrust typically lateritic that overlaps a nodular and mottled facies, originated from a saprolite of hematitic phyllite with a diffuse distribution of opaque minerals. This phyllite is one of the rocks that occur with the diamond host rocks in the old mines of the region. Both types of ferruginous duricrusts formed by relative accumulation evolve into fragmentary facies and the soil. Locally, in discordant contact, occurs a concretionary duricrust, characterized by an absolute iron accumulation mechanism.

Thermal Behavior of an AlGaN/GaN-Based Schottky Barrier Diode on Diamond and Silicon Substrates.

Devices based on AlGaN/GaN heterostructures, for example, Schottky barrier diodes (SBDs) and high electron mobility transistors (HEMTs), have been intensively investigated for applications to high-frequency and high-power areas. Presently, the substrates widely distributed are AlGaN/GaN on SiC for its high performance in radio frequency (RF) applications, for examples high cutoff frequency (fT) or high maximum oscillation frequency (fmax), and AlGaN/GaN on Si for its high power performance, for examples high breakdown voltage or high voltage operation. Chemical vapor deposition (CVD) diamond substrates have a thermal conductivity of 12 W/cm·K, and this is a remarkable point because HEMTs or SBDs on AlGaN/GaN on CVD diamonds are one of the promising alternatives for power and RF applications. In comparison, the thermal conductivity of AlGaN/GaN on a sapphire substrate is 0.33 W/cm·K while that of AlGaN/GaN on a Si substrate is 1.3 W/cm·K and that of AlGaN/GaN on a SiC substrate is 4.9 W/cm·K. In this work, we fabricated SBDs with a 137 mm Schottky channel length on AlGaN/GaN on Si and also on a CVD diamond substrate. We also compared the thermal behaviors of these fabricated large scale SBDs on Si and a CVD diamond substrate.

Radon over Kimberlite Pipes: Estimation of the Emanation Properties of Rocks (Lomonosov Diamond Deposit, NW Russia)

In this paper, using the example of the Lomonosov diamond deposit, experimental studies of rocks were carried out to assess the main radiation and physical factors affecting the formation of the radon field over the kimberlite pipes of the Arkhangelsk diamondiferous province. For various types of rocks, represented by vent kimberlites, tuffaceous-sedimentary rocks of the crater and enclosing and overlying sediments, the following were studied: porosity, density, activity of radium-226, activity of radon in a free state, level of radon production, and emanation coefficient. The research results showed that the greatest amount of radon in a free state is produced by rocks of the near-pipe space, represented by the enclosing Vendian V2 deposits and characterized by high values of the emanation coefficient, radium activity, radon production level and porosity. This fact is associated with the structural and geological features of the near-pipe space, which was exposed to the impact of kimberlite magma on the host rocks. The lowest values of these parameters are characteristic of the kimberlites of the vent facies, which limits the formation of free radon in the body of the pipe. The results of the experimental studies create prospects for the development of emanation methods for searching for kimberlite pipes in the conditions of the Arkhangelsk diamondiferous province.

Experimental Study on High-Speed Milling of SiCf/SiC Composites with PCD and CVD Diamond Tools.

Silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiCf/SiC composite) is characterized by a high strength-to-density ratio, high hardness, and high temperature resistance. However, due to the brittleness of the matrix material and the anisotropy of the reinforcing phase, it is a huge challenge for machining of the material. The milling method has advantages of a high material removal rate and applicability to complex surface geometry. However, no published literature on milling of SiCf/SiC composite has been found up to now. In this paper, high-speed milling of SiCf/SiC composites was carried out under dry conditions and cryogenic cooling using liquid nitrogen, respectively. Polycrystalline diamond (PCD) and chemical vapor deposition (CVD) diamond cutting tools were used for the milling work. The cutting performance of the two kinds of tools in high-speed milling of SiCf/SiC composites was studied. Tool failure modes and mechanisms were analyzed. The effects of the cooling approach on tool wear and machined surface quality were also investigated. The experimental results showed that under identical cutting parameters and cooling approaches, the PCD tool yielded better cutting performance in terms of a longer tool life and better surface quality than that of the CVD diamond tool. In dry machining, the failure modes of the CVD diamond tool were a large area of spalling on the rake face, edge chipping and severe tool nose fracture, whereas for the PCD tool, only a small area of spalling around the tool nose took place. Compared to the dry machining, the wear magnitudes of both PCD and CVD diamond tools were decreased in cryogenic machining. Additionally, the surface quality also showed significant improvements. This study indicates that the PCD tool is highly suitable for machining of SiCf/SiC composite, and that the cryogenic method can improve machining efficiency and surface quality.

Development of a model of a ground-penetrating radar section of a frozen rock massif with a crack

Revelance of the work. The presence of cracks significantly affects the physical and mechanical properties of rocks, which should be taken into account when planning mining operations and building mining facilities. In the conditions of the spread of permafrost rocks, characteristic of northeastern Russia, the study of fracturing is possible by the GPR method, which is used to assess the structure of rock massifs in placer deposits. The criteria for detecting cracks based on the features of wave georadar fields are currently known, and the main problem that prevents the full use of the georadar method for studying cracks in subsurface layers of rocks is the labour-consuming nature of processing and interpreting data from georadar measurements. Purpose of the work – to determine the patterns of cracks occurrence in frozen rocks in GPR wave fields. Methodology of the work. Based on the results of longstanding field work at the developed areas of alluvial diamond deposits in the Anabar region of the Republic of Sakha (Yakutia), the main elements of the radarogram structure were determined and presented in the form of a single formula. The developed formula is implemented in programs in the SCM Matlab and the results of its execution are compared with the results of modeling in the gprMax system. Results of the work and the scope of their application. The resultant formula describes the main elements of GPR radarograms quite correctly, which confirmed their comparison with the obtained model data. The correlation coefficient between the obtained matrices (Matlab and gprMax) without the low-amplitude values of multiple reflections was 0.91, which shows the identity of the structure of GPR wave fields. Conclusions. The studies carried out have confirmed the possibility of a mathematical description of the ground penetrating radar wave field obtained by sounding a mass of frozen rocks with a crack. The high correlation coefficient showed the adequacy of the developed radarogram model, which will be finalized taking into account the directional diagrams of existing georadars.

Дегазационное бурение как эффективный способ разгрузки карбонатных коллекторов вмещающих толщ коренных месторождений алмазов

The issues are considered related to gas manifestations during the development of primary diamond deposits in Yakutia — «Internatsionalnaya» and «Udachnaya» pipes, which are the most difficult in terms of gas-dynamic conditions. Gas manifestations at the field are associated to a greater extent with gases dissolved in the natural brines, and to a lesser extent — with free and sorbed gases. Due to the fact that when developing the underground mines, the sources of explosive gases were recorded, to ensure the safe conduct of mining operations it is required to unload the rock mass. Analysis of data obtained at the different stages of construction and operation of the fields identified the source of the recorded gas manifestations: reservoirs and local gas reservoirs filled with gas-saturated brines. It was revealed that the sources of gas release are zones consisting of cavernous and fractured carbonate rocks complicated by fracturess and low-amplitude tectonics. The analysis of the dynamics of changes in the gas-dynamic, hydrogeological and mining-geological conditions of mines allowed to propose a two-stage advanced degassing of the host rocks as a rather effective method of combating gas manifestations. At the first stage, vertical advance wells are drilled for the entire capacity of the production block. At the second stage, 3–7 horizontal and slightly inclined (up to 10°) wells are drilled in front of the borehole of the underground working under construction. Thus, there is an interval unloading of the massif and the involvement of undeveloped natural gas reserves at the first stage. Actual observations of gas inflows in the underground mine workings showed a significant drop in gas production rates. In such a way, at the «Internatsionalnaya» mine the average gas flow rate per well (per year) decreased from 12.67 to 1.06 m3/h, which confirms the success of the selected two-stage degassing.

A strategist and innovator in arranging systematic ore studies for diamond, precious and base metal deposit development

A strategist and innovator in arranging systematic ore studies for diamond, precious and base metal deposit development

Typomorphic properties of kimberlite indicator minerals and their use in forecasting diamond deposits on the Siberian Platform

The results of mantle nodule investigations in kimberlite diatremes of the main Siberian Platform diamondiferous regions were analyzed. Morphology and chemistry of garnets, chrome-diopsides, clinopyroxenes, olivines, picro-ilmenites, chromites, chrome-spinellids and diamonds were investigated in detail. Generally, the quantity of diamond association minerals is proportional to diamond potential of a certain kimberlite variety for each type of kimberlite rocks composing pipes.

BACKGROUND STATE OF THE FISH FAUNA IN THE ZIMNYAYA ZOLOTITSA AND SOYANA RIVERS (ARKHANGELSK REGION) UNDER INDIRECT IMPACT FROM DIAMOND MINING

The study focused on the species and taxonomic diversity of fish in the catchments of rivers Zimnyaya Zolotitsa and Soyana (White Sea-Kuloy plateau), exposed to indirect im pact from diamond mining in the Arkhangelsk Region. Faunal complex affiliations, ecological characteristics of nutrition and natural reproduction (spawning substrates and egg deposition methods) of the fish were revealed. The families with the greatest number of species were Coregonidae in the Zolotitsa catchment, and Cyprinidae in the Soyana catchment. All fish inhabiting the two catchments compared belonged to 5 faunal complexes, with a prevalence of arctic freshwater species in the Zolotitsa catchment, and boreal piedmont species in the Soyana catchment. In dietary terms, the species falls into four groups: plankton-feeders, benthos-feeders, predators (including the parasitic predation of lampreys), and euryphagous, the latter two quantitatively prevailing in both catchments. In terms of reproduction characteristics, the largest number of species in both the Zolotitsa and the Soyansa catchment spawn in stony-sandy bottom areas, being litho- and psammophiles in relation to the spawning substrate. The economic value of the fish fauna was determined, and rare, regionally red-listed fish species were identified. Data on the current composition of the fish fauna can be used as background information in a comprehensive assessment of the impact of mine-and-mill operations during industrial-scale development of diamond deposits on river ecosystems.

In-situ deposition of diamond on functionally graded copper scaffold for improved thermal conductivity and mechanical properties

A novel functionally graded structure of diamond was developed with significantly enhanced thermal conductivity and compressive strength, based on synergistic effects combining chemical vapor deposition (CVD) and selective laser melting (SLM). In-situ diamond growth was achieved without conventionally complex pretreatment steps thanks to the high surface roughness of as-printed graded copper scaffold. The continuous diamond film coated on graded copper scaffold forms a monolith with interconnected network, acting as an effective layer for heat conduction with an exceptional increase (459%) in thermal conductivity compared with copper counterpart. The functionally graded structure also demonstrates a progressive mechanical response to loading compared with the uniform structure. This work opens a new avenue for realizing three-dimensional diamond structure and proves its multifunctionalities, especially for high-power electronics applications.

Особенности ведения взрывных работ при освоении минеральных ресурсов северных и арктических районов России

A priority task for facilitating the development of the Arctic zone of the Russian Federation is to design new blasting technologies to be efficiently used in extremely difficult climatic, mining and geological conditions at remote operations. This is further motivated by the fact that up to 40% of Russia's gold reserves, 60–90% of its natural gas resources and 100% of its primary diamond deposits are located in the Arctic zone. The article analyses the problems of blasting operations while developing deposits in the Arctic zone. The main formulations of ordinary explosives are reviewed that allow to solve a number of challenges associated with blasting operations in remote and hard-to-reach Arctic regions. Based on the performed analysis of existing methods, further areas of research are identified that can improve the quality and safety of blasting operations: 1) determination of optimum weight and dimensions of boosters based on ordinary explosives depending on the initiating borehole size; 2) determination of the relation between the particle size / composition of the booster and the detonation velocity; 3) determination of physical parameters of transition from deflagration to detonation and gaining sensitivity to the initiating pulse from the detonator cap by the ordinary explosive compositions.

Imaging and Modeling C2 Radical Emissions from Microwave Plasma-Activated Methane/Hydrogen Gas Mixtures: Contributions from Chemiluminescent Reactions and Investigations of Higher-Pressure Effects and Plasma Constriction.

Wavelength and spatially resolved imaging and 2D plasma chemical modeling methods have been used to study the emission from electronically excited C2 radicals in microwave-activated dilute methane/hydrogen gas mixtures under processing conditions relevant to the chemical vapor deposition (CVD) of diamond. Obvious differences in the spatial distributions of the much-studied C2(d3Πg-a3Πu) Swan band emission and the little-studied, higher-energy C2(C1Πg-A1Πu) emission are rationalized by invoking a chemiluminescent (CL) reactive source, most probably involving collisions between H atoms and C2H radicals, that acts in tandem with the widely recognized electron impact excitation source term. The CL source is relatively much more important for forming C2(d) state radicals and is deduced to account for >40% of C2(d) production in the hot plasma core under base operating conditions, which should encourage caution when estimating electron or gas temperatures from C2 Swan band emission measurements. Studies at higher pressures (p ≈ 400 Torr) offer new insights into the plasma constriction that hampers efforts to achieve higher diamond CVD rates by using higher processing pressures. Plasma constriction is proposed as being inevitable in regions where the local electron density (ne) exceeds some critical value (nec) and electron-electron collisions enhance the rates of H2 dissociation, H-atom excitation, and related associative ionization processes relative to those prevailing in the neighboring nonconstricted plasma region. The 2D modeling identifies a further challenge to high-p operation. The radial uniformities of the CH3 radical and H-atom concentrations above the growing diamond surface both decline with increasing p, which are likely to manifest as less spatially uniform diamond growth (in terms of both rate and quality).

Chemical vapor deposition diamond dental burs for high speed air turbine handpieces

Abstract Background The objectives were, establishment of diamond coating using Chemical Vapor Deposition (CVD) on tungsten carbide burs and, assessment of diamond film adherence at 250,000 rpm after cavity preparations on teeth. Methods Hot Filament CVD (HFCVD) was used to deposit a thin diamond film on tungsten carbide burs using 1–1.5% methane in excess hydrogen at 1800–2200 °C and 2700 - 6700 Pa pressure. Consistent and repeated film deposition of Microcrystalline diamond (MCD) and Nano crystalline diamond (NCD) could be achieved. Raman spectrometry and scanning electron microscopy (SEM) were used to confirm diamond deposition. Adherence of the films was checked after cavity preparations on human teeth at speeds of ~250,000 rpm, and flank wear was determined using SEM. Results SEM images confirmed presence of microcrystalline and nanocrystalline forms. MCD had a 3–7 μm cubo-octahedral crystal formation. NCD was seen as 25–50 nm cuboidal facets in columnar formation. Raman spectrometry corroborated these findings. SEM of NCD showed no loss of diamond film or blunting of blades after three cavity preparations followed by a maximum loss of 33 μm after nine repeated cavity preparations. MCD showed partial loss of diamond film after third cavity with a maximum loss of 91 μm after nine repeated cavities. Conclusion Successful deposition of uniform diamond coating on tungsten carbide burs that remain adherent even at high rotational speeds was achieved and NCD coating adhered better compared to MCD. Practical implication The newly developed dental bur which combines the cutting action of bladed instruments and the hardness of diamond and provides a new area of clinical application.

A new pyrope-based mineralogical-petrological method for identifying the diamond potential of kimberlite/lamproite deposits

• Fluid compositions can be additional indicator of the carbon formation in petrology. • Optimum conditions for diamond growth and preservation correspond to water-rich fluid. • Estimated fluid of the main part of the high diamond grade pipes corresponds to water-rich fluid. • Calculated fluid compositions from EMP pyrope analyses can be used in the prospecting of diamond deposits. P-T- Oxygen fugacity (fO 2 ) conditions and fluid compositions were estimated for the formation conditions of pyrope garnet inclusions in diamonds and xenocrysts from diamond-bearing and diamond-free kimberlites using their total chemical analyses and single oxythermobarometry. Our data indicate that optimal conditions for diamond growth and preservation occur in the presumed water-rich mantle fluids containing the lowest abundance of free atomic carbon. The majority of the calculated C-H-O fluid compositions for diamond formation in peridotite xenoliths from high diamond grade kimberlites correspond to a high hydrogen and low carbon and oxygen atomic fluid percents, while those from the majority of peridotite xenoliths in the low grade diamond kimberlites corresponds to the low hydrogen, high carbon and oxygen atomic percent fluids. This new approach defines the conditions of diamond formation for kimberlitic deposits. It better characterizes diamond grades in kimberlites in comparison to the previous empirical mineralogical Ca-Cr methods and can be used as a more precise mineralogical-petrological method for prospecting for kimberlitic diamond deposits.